Versatile polyacrylamide/gum hybrid hydrogels for tunable mechanics and high-fidelity 3D extrusion printing

Polyacrylamide (PAM) hydrogels are widely used in biological research for their well-established and tunable mechanical properties, which can closely match native tissue stiffness, making them attractive for mechanobiology, biosensing and tissue engineering. However, extrusion-based 3D printing of PAM remains challenging due to the inherently low viscosity of precursor solutions. Existing strategies reach printable viscosities with rheology modifiers such as Laponite clays or protein-based microgels, but these additives strongly couple printability to final stiffness, substantially increasing the elastic modulus and compromising the soft, tunable character that makes PAM valuable. Here, we present a novel yet accessible one-pot strategy for extrusion-printable PAM hydrogels, using natural polysaccharide gums as a distinct class of rheology modifier. Unlike conventional additives, gums confer the shear-thinning and viscoelastic structure required for extrusion at low concentrations (2-4 w/v %), while preserving the established AM/BIS-stiffness relationship and allowing modulus to be tuned independently through monomer concentration. Tragacanth, xanthan, and guar gums were systematically evaluated across concentrations for their effects on ink rheology, print fidelity, and mechanics. High-fidelity printing was achieved at concentrations as low as 2 w/v % for guar and 3 w/v % for tragacanth and xanthan. Mechanical characterization reveals soft, tunable properties, with elastic moduli from 5 to 58 kPa across gum type and concentration, spanning a broad range of soft tissue stiffnesses. Guar and tragacanth in particular produced moduli statistically comparable to pure PAM, confirming minimal impact on network mechanics. Preliminary cytocompatibility assays confirm these hybrid hydrogels support MDCK I cell viability. We further demonstrate core-shell extrusion printing of PAM/gum hydrogels for the first time, using a sacrificial core to generate hollow, perfusable channels down to ~200 µm in diameter. Together, these results establish PAM/gum hydrogels as a printable, mechanically tunable ink platform, laying a materials-processing foundation for architecturally complex, channeled PAM-based constructs.